The present invention relates, in general, to a rolling machine for rolling a metal container with a longitudinal seam, in particular a sheet steel container.
Typically, a cylindrical body, as intermediate product, is bent from a flat metal plate, with adjacent or overlapping butt edges securely joined to one another by folding or welding. Subsequently, a disk-shaped lower bottom and, optionally, a respective upper bottom, is welded or folded to the cylindrical body to form a closed container or, optionally, an open-topped container. Conventional sheet steel containers suffer shortcomings because the inside welding seam edge is oftentimes a cause of premature rust formation and contamination of the contents.
In order to address this problem, German Pat. No. DE 196 37 107 A1 proposes a flattening and smoothing of the welding seam and the overlapping material area by employing a rolling machine so that application of a paint is possible and the formation of clusters of rust, in particular in the interior of the container along the welding seam, can substantially be eliminated. The rolling machine described in German Pat. No. DE 196 37 107 A1 includes a rolling drum, which is secured on the outside to a free cantilevered arm. This arm has to absorb great forces and thus is configured of substantial size to prevent flexure. In order to enable a continuous production, the cantilevered arm is rotatably supported whereby disadvantageously great masses need to be moved in short time intervals.
It is an object of the present invention to provide an improved rolling machine, obviating the afore-stated drawbacks.
In particular, it is an object of the present invention to provide an improved rolling machine for processing metal containers with longitudinal seams, which realizes high production speeds, without requiring a swinging or rotating of large machine components so as to eliminate a need to move masses.
These objects, and other which will become apparent hereinafter, are attained in accordance with the invention by configuring the rolling machine as linear continuous rolling machine which includes an upper carrier frame; an upper rolling drum rotatably supported in the upper carrier frame; a lower drum stand; and a driven lower rolling drum rotatably mounted in the lower drum stand. In accordance with the present invention, the upper carrier frame for acting on the inside surface of the body is supported in a so-called xe2x80x9cfloatingxe2x80x9d manner, i.e. connected to the lower drum stand in an alternating manner by first and second locking devices.
As the result of the rolling process over the entire body length or along the entire longitudinal welding seam or folding seam of the container, the adjacent or overlapping butt edges of the cylindrical body, i.e. envelope, are closed (filled) in the area of the longitudinal welding seam and the rebounding gusset zone inside as well as outside along the overlapping end edges through material displaced laterally in circumferential direction by the rolling process, and disappear. As a consequence, easy application of paint, in particular the interior painting, or of a powder coating is ensured even in this otherwise very critical zone. Through the provision over a smooth, continuous paint coat, the area of the welding seam or fold is no longer recognizable and the above-stated drawbacks are eliminated.
The transport or the forward motion of the sheet metal body (envelope) in the welding machine is typically realized by a corrugated feed roller which engages in the area of the overlap region. During passage of the body, the individual corrugations are pressed into the material to create an unsightly fluting. By smoothing the area of the longitudinal seam of the sheet metal body in accordance with the invention, also this fine fluting disappears.
In accordance with the present invention, the overlapping wall area of the cylindrical envelope is rolled flat along the longitudinal seam of a longitudinally welded container from about twice the strength to at least 1 xc2xd times of the strength or to the normal single strength of the metal plate or to the wall strength of the body. Thereby, the rolling process is suitably carried out in immediate succession of the welding procedure at still elevated temperature of the material of the longitudinal seam area to be rolled, thereby smoothing all uneven zones. In particular in conjunction with large-volume containers, such as e.g. a 220 liter steel drum with a drum wall height or welding seam length of approximately 900 mm, smoothing of the longitudinal seam results in a substantial improvement of the product quality.